1. Field of the Invention
The present invention relates to printer shuttle drives, and more particularly to printer shuttle drives in which a cam is employed to drive the shuttle in reciprocating fashion.
2. History of the Prior Art
It is known to drive a shuttle within a printer using a rotating cam. An example of a dot matrix line printer in which a hammer bank-carrying shuttle is driven in reciprocating fashion by a generally oval-shaped cam is provided by U.S. Pat. No. 3,941,051 of Barrus et al. In the printer shown in the Barrus et al patent the shuttle which is mounted so as to be capable of undergoing linear motion is coupled to the rotating cam by a rotatable, generally cylindrical cam follower. As the generally oval-shaped cam rotates, the cam follower which bears on the outer surface of the cam under spring pressure moves the attached shuttle back and forth along its linear path of travel in reciprocating fashion. Simultaneously, a counterbalancing mass which is also driven by the rotating cam is caused to undergo reciprocating motion in an opposite sense from the shuttle so as to counterbalance the reciprocating shuttle and thereby minimize or eliminate vibration or other unwanted motion which might otherwise result.
In cam shuttle drives of the type described in previously referred to U.S. Pat. No. 3,941,051 of Barrus et al, the cam follower must be aligned with the cam so that the axis of rotation of the cam follower is parallel or nearly parallel with the axis of rotation of the cam. If the cam follower becomes skewed such that the axis of rotation thereof is no longer generally parallel with the axis of rotation of the cam, a side thrust on the cam follower assembly results. The cam follower assembly which is typically made so as to be capable of withstanding substantial longitudinal loads on the order of 130 pounds or greater is usually not capable of withstanding much side thrust. The side thrust which results from a skewed condition of the cam follower relative to the cam may result in overheating, eventual scoring of the camming surfaces and even eventual failure of the cam or the follower assembly.
Careful adjustment of the shuttle mount so as to properly align the cam follower with the cam will usually minimize if not eliminate harmful side thrusts and the problems associated therewith. However, even where careful adjustment is periodically made, alignment can change for various reasons, particularly with prolonged use of the printer. This results in the possibility of damage if misalignment occurs and persists.
Accordingly, it would be desirable to provide a cam follower assembly for a cam shuttle drive which is essentially self-aligning so as to greatly minimize or eliminate unwanted side thrusts. It would furthermore be desirable to provide a cam drive arrangement in which the cam follower assembly employed to drive a counterbalancing mass from the same common cam that drives the shuttle is also self-aligning in nature.